I was wondering what is the best thing to do with fish during the winter? I know it probably has a lot to do with the overall depth of the pond. If one does decide to winter their fish is there anything special someone should be concerned with?

Hello -
Good question. I have been asked this question a lot lately. I am currently working on a "Winterization of Fish" page for my website to address this question in great detail. For now I will post a shorter version to answer your question.

When over wintering fish you have two options. A. Bring the fish indoors or B. Leave the fish in the pond.

A. Indoors
When you bring the fish indoors, your fish care really depends on the temperature of the water. If you bring them indoors and keep that at a temperature above 50 degrees Fahrenheit you need to treat them just as though they are still in your summer pond. You need to feed them ( the colder the temperature the less you should feed them), supply them with oxygen (via a air stone) and provide them with good filtration. Very often the pond volume is greater than your holding tank indoors. This means more fish will be packed into a smaller area, making oxygen supply and good filtration even more important.
If this is a concern, I would advise keeping your fish in a state of hibernation during the winter. Place them in your garage where the temperature stays below 50 degrees Fahrenheit and the tank does not ice over. This will slow down their metabolism and will require you to NOT feed your fish. This means not as much fish waste and you don't have to worry about uneaten food bogging down your filtration capacity. You still do need to provide oxygen for them, which can be achieved by placing a small aquarium air stone inside of the tank.

B. Outdoors
Depth - The success of over wintering you fish outdoors does depend on several factors. You are right in your assumption that depth plays a major role. Some experts recommend a depth of 24 to 48 inches deep. Anything less than 24 inches may require additional heat for the ice may become too thick. Where I life in Faribault, Minnesota there is a city ordinance where 30 inches is the deepest a pond contractor can dig before it is considered a "pool." This means that a gate must be built around the pond. We try to stay around the 30 inch mark to give customers the ability to over winter fish outdoors.
Gas Exchange - You are required to create a hole in the ice no matter what depth of a pond you have. The hole allows for toxic gasses to escape from under the ice. The hole can be kept open in 3 main ways.

1.) Pump - A pond pump can be placed in the middle of the pond to help "boil" the water surface to keep it from freezing. I would not recommend a very large pump for this will cause the temperature layers of the water to mix and will bring the temperature of the water down.

2.) Floating De-icer - This device heats keeps a hole in the ice through the use of heating coils. It does not heat the entire pond but rather heats up a small section of the water on the top. This keeps the ice from freezing over.

3.) Aerator - A air pump attached to an air stone is another way to keep the pond open as well as supply oxygen. The aerator should be placed towards the top of the water column. This will prevent the temperature layers of the water from mixing (resulting in a colder pond).

You will still want to keep a close eye on your pond throughout the winter. Aerators and pumps may move out of position, your de-icer may become unplugged, or extreme cold temperatures may test your devices to their limit.

I am currently testing different de-icers and aerators. I am also testing water temperature at different levels in the pond.

I will be posting some of my results in the coming weeks.

Thanks for your question. If you have any more don't be afraid to ask away!

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